The idea behind the dormant Commerce Clause is that this grant of power implies a negative converse—a restriction prohibiting a state from passing legislation that improperly burdens or discriminates against interstate commerce. The restriction is self-executing and applies even in the absence of a conflict between state and federal statutes, but Congress may allow states to pass legislation that would otherwise be forbidden by the dormant Commerce Clause.

Sounds to me like that is an undue burden on interstate commerce, and should not be enforceable.